Journal of Dental Medicine

Statement of Problem: One of the greatest problems in metal –ceramic restorations is debonding of porcelain from dental alloys. Production of dental alloys by Iranian companies necessitates the evaluation of physical and handling properties of these products.

Purpose: In this study the bond strength between porcelain and two types of base metal alloys, Supercast (with beryllium) and Minalux (without beryllium) was investigated.

Materials and Methods: In this experimental study 10 cylindric bars from each base metal alloy were prepared. The bars were degassed and porcelain was applied around them in a disc form (8 mm diameter and 2 mm thickness). The bond strength of porcelain to metal bars was tested with the shear strength test by Instron. Data were analyzed with student t-test and P<0.05 was considered as the limit of significance.

Results: The mean failure load was 71.58±6.4 KgF for Supercast and 67.34±5.48 for Minalux alloy. The bond strength of Supercast and Minalux were 55.85±4.99 MPa and 52.54±4.27 MPa respectively. The difference was statistically significant (P0.001).

Conclusions: This study showed that nickel-chromium-beryllium alloy (Supercast) produced significantly better ceramometal bonding than nickel chromium alloy without beryllium (Minalux).

Statement of Problem: Ceramic restorations are popular because they can provide the most natural replacement for teeth. However, the brittleness of ceramics is a primary disadvantage. There are various methods for strengthening ceramics such as metal framework, ceramic cores, and surface strengthening mechanisms through glazing, work hardening and ion exchange.

Purpose: The purpose of this study was to evaluate the effect of polish on flexural strength of feldspathic porcelain and to compare it with overglaze and autoglaze.

Materials and Methods: In this experimental study, one brand of feldspathic porcelain (colorlogic, Ceramco) was used and forty bars (25×6×3 mm) were prepared according to ISO 6872 and ADA No. 69. The specimens were randomly divided into four groups: overglazed, auto glazed, fine polish and coarse polish (clinic polish). Flexural strength of each specimen was determined by three point bending test (Universal Testing Machine, Zwick 1494, Germany). Collected data was analyzed by ANOVA and post-hoc test with P<0.05 as the limit of significance.

Results: A significant difference was observed among the studied groups (P<0.0001). According to post-hoc test, flexural strength in overglaze and fine polish group were significantly stronger than clinic polish and autoglaze group (P<0.001). Although the mean value for overglazed group was higher than fine polish group, this was not statistically significant (P=0.9). Also no statistical difference was seen between autoglazed and coarse polish group (P=0.2).

Conclusion: Based on the findings of this study, flexural strength achieved by fine polish (used in this study) can compete with overglazing the feldespathic porcelains. It also can be concluded that a final finishing procedure that involves fine polishing may be preferred to simple staining followed by self-glazing.

Background and Aim: All ceramic, inlay-retained resin bonded fixed partial denture is a conservative method for replacement of missing teeth, because of minimal tooth reduction. The connector between the retainer and the pontic is the weak point of these bridges. Reinforcement of ceramic core will increase the clinical longevity. The aim of this study was to determine the effect of zirconia on flexural strength of IPS Empress 2 core ceramic.

Materials and Methods: In this experimental in vitro study, twenty eight bar shape specimens (17´3.1´3.1 mm) were made of four different materials: (1) Slip casting in-ceram alumina core (control group) (2) Hot-pressed lithium disilicate core ceramic (IPS Empress 2) (3) IPS Empress 2 with cosmopost (zirconia post) inserted longitudinally in the center of the bar (4) IPS Empress 2 with cosmopost (zirconia post) inserted longitudinally in bottom of the bar. Specimens were subjected to three-point flexure loading with the span of 15mm, at a cross-head speed of 0.5 mm/min. Failure loads were recorded and analyzed using one-way ANOVA and Tomhane Post-hoc tests and p<0.05 was set as the level of significance. Fractured surfaces were then observed by scanning electron microscope (SEM). Four additional samples were made as the third group, and zirconia-IPS interface was observed by SEM before fracture.

Results: Mean values and standard deviations of three point flexural strengths of groups 1 to 4, were: 378.4±44.6, 258.6±27.5, 144.3±51.7, 230±22.3 MPa respectively. All the groups were statistically different from each other (P<0.05), except groups 2 and 4. The flexural strengths of groups 2, 3, 4 were significantly lower than group 1. Group 3 had the lowest flexural strength. SEM analysis showed that the initiated cracks propagated in the interface of zirconia post and IPS Empress 2 ceramic.

Background and Aim: Replacing fractured ceramometal restorations may be the best treatment option, but it is costly. Many different bonding systems are currently available to repair the fractured ceramometal restorations. This study compared the shear bond strength of composite to a base metal alloy using 4 bonding systems.

Materials and Methods: In this experimental in vitro study, fifty discs, casted in a Ni-Cr-Be base metal alloy (Silvercast, Fulldent),were ground with 120, 400 and 600 grit sandpaper and divided equally into 5 groups receiving 5 treatments for veneering. Conventional feldspathic porcelain (Ceramco2, Dentsply Ceramco) was applied on control group (PFM or group1) and the remaining metal discs were air- abraded for 15 seconds with 50 mm aluminum oxide at 45 psi and washed for 5 seconds under tap water.Then the specimens were dried by compressed air and the  groups were treated with one of the bonding systems as follows: All-Bond 2 (AB), Ceramic Primer (CP), Metal Primer II (MP) and Panavia F2 (PF). An opaque composite (Foundation opaque) followed by a hybrid composite (Gradia Direct) was placed on the treated metal surface and light cured separately. Specimens were stored in distilled water at 37⁰C and thermocycled prior to shear strength testing. Fractured specimens were evaluated under a stereomicroscope. Statistical analysis was performed with one way ANOVA and Tukey HSD tests. P<0.05 was considered as the level of significance.

Results: Mean shear bond strengths of the groups in MPa were as follows: PFM group 38.6±2, All-Bond 2 17.06±2.85, Ceramic Primer 14.72±1.2, Metal Primer II 19.04±2.2 and Panavia F2 21.37±2.1. PFM group exhibited the highest mean shear bond strength and Ceramic Primer showed the lowest. Tukey's HSD test revealed the mean bond strength of the PFM group to be significantly higher than the other groups (P<0.001). The data for the PF group was significantly higher than AB and CP groups (P<0.05) and the shear bond strength of the MP group was higher than CP group, but was not significantly different from AB (P>0.05).

Conclusion: Based on the results of this study, the most reliable treatment for fractured metal-ceramic restorations would be the replacement of the restoration. If this is not possible, adhesive resin cements containing filler and phosphate-based monomers (especially MDP) such as Panavia F2 could be recommended for bonding composite to base metal alloys.

Background and Aim: Polymerization shrinkage of resin cements during setting leads to stress on teeth receiving indirect esthetic restorations. Some methods like blocking out undercuts during cavity preparation with glass Ionomer can reduce the mass of resin cement and therefore the amount of stress. The aim of this study was to evaluate the fracture resistance of molar teeth, receiving class I ceramic inlays with two different methods of blocking out undercut.

Materials and Methods: In this experimental study, thirty intact molar teeth were randomly divided into three groups of 10 each. One group was maintained intact as the control group. Similar class I cavities with identical undercuts were prepared on the other groups. In group 2 the undercut was filled with light cured glass Ionomer (vitremer 3M) before making impression, and in group 3 they were blocked out in the lab before preparation of the inlay. All the teeth in test groups were restored with indirect ceramic inlays.(vitadur - Alpha/ single bond / Rely X ARC). After thermocycling load causing fracture was assessed by universal testing machine. All the specimens were examined under a steriomicroscope (X40) to determine type of fracture. The results were analyzed by one way ANOVA and Tukey HSD tests. P< 0.05 was considered as the level of significance.

Results: The restored groups showed significantly less fracture resistance than the control group. The difference between two test groups was not significant. The fracture in group2 had less destruction.

Conclusion: According to the findings of this study, blocking out the undercut with two different methods (using glass ionomer/ or blocking it out on the die) made no diferrence in fracture resistance.

Background and Aims: Metal-free and fiber-reinforced composite (FRC) restorations have drawn considerable attention and interest in recent years for restoring in the posterior area due to their improved esthetics. Fracture resistance is one of the most important mechanical properties of materials because of 500-600 N load of occlusion. The restorations should tolerate this load. The purpose of this in vitro study was to compare the fracture resistance of FRC with that of zirconia all-ceramic for posterior partial dentures.

Materials and Methods: Forty extracted human intact teeth (20 first premolars and 20 first molars) selected for fabricating 10 pairs of fiber-reinforced composite and 10 pairs of zirconia all-ceramic bridges. After receiving standard tooth preparation, the teeth were mounted with 7.5 mm distance between each other. The bridges were made and cemented on the teeth. Then the restorations were stored in 37ºC water for 30 days. The fracture resistance was measured using mechanical testing machine with cross-head speed of 1mm/min. Data were evaluated by Independent Sample T test.

Results: The mean fracture resistance in the ceramic group was 1329.41 N and for the F.R.C group was 1118.528 N with significant differences between them (P=0.034). The failure modes were mainly cohesive at pontic area for ceramic samples, but adhesive for FRC samples at pontic area.

Conclusion: Both systems showed sufficient fracture resistance for using in posterior area.

Background and Aims: The aim of this study was to evaluate the effect of zirconia and base metal cores on the color of restorations. Furthermore, the effect of different backings on the color of cercon zirconia was evaluated.
Materials and Methods: The specimens were Cercon zirconia and metal ceramic discs with "high Au" and "base metal" alloys. Cercon zirconia discs were veneered with veneering shade of A2 and two thickness of porcelain (0.7 mm, 1.2 mm). There were 3 discs in each group. Metal ceramic discs were made of "nickel-chromium" alloy (Verobond) and "high Au" alloy (World 89) and two shades (A2, A3.5) and two thicknesses of veneering porcelain. 3 types of backing (high Au, nickel-chromium and A3 shade composite) were made for Cercon zirconia discs. Spectrophotometric evaluation of zirconia discs (on 3 backings) and metal ceramic discs was done. One-way ANOVA and Tukey tests were used for data analysis.
Results: There were no significant differences between the amounts of L*, a*, b* for Cercon zirconia on different backings (P>0.05). In comparison between different core groups, a* was significantly higher in metal ceramic groups compared with that of zirconia groups (P<0.05).
Conclusion: Cercon zirconia can completely mask the underlying backing.

Background and Aims: Reliable bonding between tooth substrate and zirconia-based ceramic restorations is always of great importance. The laser might be useful for treatment of ceramic surfaces. The aim of the present study was to investigate the effect of laser irradiation on the shear bond strength of zirconia ceramic surface to dentin.

Materials and Methods: In this experimental in vitro study, 40 Cercon zirconia ceramic blocks were fabricated. The surface treatment was performed using sandblasting with 50-micrometer Al2O3, CO₂ laser, or Nd:YAG laser in each test groups. After that, the specimens were cemented to human dentin with resin cement. The shear bond strength of ceramics to dentin was determined and failure mode of each specimen was analyzed by stereo-microscope and SEM investigations. The data were statistically analyzed by one-way analysis of variance and Tukey multiple comparisons. The surface morphology of one specimen from each group was investigated under SEM.

Results: The mean shear bond strength of zirconia ceramic to dentin was 7.79±3.03, 9.85±4.69, 14.92±4.48 MPa for CO₂ irradiated, Nd:YAG irradiated, and sandblasted specimens, respectively. Significant differences were noted between CO₂ (P=0.001) and Nd:YAG laser (P=0.017) irradiated specimens with sandblasted specimens. No significant differences were observed between two laser methods (P=0.47). The mode of bond failure was predominantly adhesive in test groups (CO₂ irradiated specimens: 75%, Nd:YAG irradiated: 66.7%, and sandblasting: 41.7%).

Conclusion: Under the limitations of the present study, surface treatment of zirconia ceramics using CO₂ and Nd:YAG lasers was not able to produce adequate bond strength with dentin surfaces in comparison to sandblasting technique. Therefore, the use of lasers with the mentioned parameters may not be recommended for the surface treatment of Cercon ceramics.

Background and Aims: Since a large marginal opening allows more plaque accumulation, gingival sulcular fluid flow and bone loss, microleakage, recurrent caries and periodontal disease, marginal fit is of great importance in fixed restorations. The aim of this study was to compare the marginal fit of zirconium-based all ceramic (Cercon) frameworks, made by two different approaches (Direct and Wax-up scanning).

Materials and Methods: An abutment analog, with 5.5 mm width and height, was selected as an experimental model. Twenty all ceramic cores were made for this model (10 specimens per each group). In the first group (Direct), experimental models were scanned directly using Computer Aided Design/Computer Aided Manufacturing (CAD/CAM). The core was then designed with the aid of a computer and machined. In the second group (Wax-up or CAM) a wax-up pattern was made on the experimental model and then scanned and milled from Cercon blocks. The marginal discrepancy of each specimen was recorded using a stereomicroscope (SZX9, Olympus, Japan) and digital camera (Mode TK, C1380E, JVC, Japan) and then measured by Adobe Photoshop CS software. The data were analyzed using T-test.

Results: Mean marginal discrepancy of Direct group (85.2±3.95 µm) was significantly less than that of Wax-up group (120.2±6.91 µm).

Conclusion: Improved marginal fit of zirconia ceramics was found with the direct model scanning compared with that of Wax-up scanning using CAD/CAM.

Background and Aims: The purpose of this in vitro study was to assess the effect of two different surface treatments on the contrast ratio of IPS e.max press ceramic submitted to accelerated aging.

Materials and Methods: Ten ceramic (IPS e.max Press) disks (10-mm diameter and 1.5-mm thick) were fabricated according to the manufacturer's recommendations. The samples were randomly divided into 2 groups (n=5): polishing and glazing. Contrast ratio ware obtained with a spectrophotometer before and after accelerated aging. The contrast ratio (CR=Yb/Yw), was defined as the ratio of illuminance (Y) of the test material when it is placed on the black background (Yb) to the illuminance of the same material when it is placed over a white background (Yw), was determined. The data were statistically analyzed by two-way analysis of variance (P<0.05).

Results: All specimens of IPS e.max press ceramic showed significant increase in CR after 300-hour accelerated aging time (P=0.005). Polished samples showed significantly higher opacity compared with that of the glazed ones (P=0.018).

Conclusion: Within the limitations of this study, it may be concluded that the glazed specimens showed higher stability in their translucency than the polished specimens.

Background and Aims: The marginal integrity of fixed restorations always is a major matter of concern for dental clinicians. Any cause of distortion, including veneering processes, in the marginal integrity is supposed to be detrimental for long-term success of fixed dental prostheses. The aim of this in vitro study was to compare the marginal adaptation of two different full ceramic restoration systems (Zirkouzahu&Cercon) and possible changes in marginal integrity following the multiple veneering process.

Materials and Methods: Twelve all-ceramic crowns in the form of coping were fabricated on a pre-made standard metal die with finish line of shoulder preparation from two commercial systems: Cercon® and Zirkonzahn®. The specimens were not cemented. The Crown/Die discrepancy were measured by means of a precise stereo microscope (accuracy±0.1 μm), at various points (n=12) selected along circumferential margin of the restorations. Same procedure was accomplished after applying the veneering porcelain. The mean gap dimensions were calculated and data were analyzed by multivariate (b) test.

Results: Mean marginal gap dimensions before and after veneering porcelain firing cycles, for Cercon® were (59.67±13.46 µm) and (63.75±14.16 µm) and for Zirkonzahn® were (65.81±24.37 µm) and (64.74±21.94 µm), respectively. Hotelling trace Multivariate(b) test method showed that the rate of mismatching marginal integrity in two groups (Cercon® and Zirkonzahn®) had no significant difference before and after porcelain firing (P>0.05).

Conclusion: Within the limitation of this study, the marginal integrity of both systems were seems to be within the clinically acceptable standard dimension, i.e. 120μm.The marginal gap of both all-ceramic systems were not affected by veneering porcelain firing cycles.

  Background and Aims: Nowadays, the application of all ceramic restorations are being raised, because of their physical characteristics, such as translucency and good appearance. Numerous researchers investigated the impact of surface treatments on the bond strength of zirconia ceramic with resin cements. The aim of this study was to compare the microshear bond strength of Cercon and Zirkonzahn (two kind of zirconia) ceramics, to two types of resin cements after thermocycling.

  Materials and Methods: In this study, 24 rectangular specimens were made from each group of Cercon and Zirkonzahn ceramics. After sandblasting, these specimens were connected to 3×1 mm² composite cylinders by two resin cements (Panavia F₂ and Rely X Unicem₂). After performing a thermocycling regime for 5000 cycles (5-55 ◦ C), the microshear bond strengths were measured by a universal testing machine. The mode of failures were determined by a stereomicroscope. Data were analyzed using two-way ANOVA.

  Results: Type of ceramics had no significant impact on the microshear bond strength (P=0.317). The highest bond strengths in both ceramics were obtained with Reply X Unicem (P=0.035). The predominant failure mode was adhesive between the cement and ceramic.

  Conclusion: Type of resin cement had a significant effect on their bond strengths to zirconia ceramics.

  Background and Aims: The aim of this review article was to present the information have been published, regarding the functional properties of Zirconia until today.

  Materials and Methods: A review of the literature was carried out in MEDLINE database using key words (Dental ceramic, Zirconia, 3Y-TZP, Clinical performance, Machining and Transformation toughening). These searches were limited to the articles published after the year 2000.

  Conclusion: Despite excellent clinical results in short-term studies, there is still a major need to have more clinical and laboratory long-term information about zirconia restorations.

  Background and Aims: Tooth crowning often leads to changes in periodontal index through changes in emergence profile zone. The purpose of this study was to compare the effect of metal-ceramic with that of
All-Ceramic restorations on the plaque a accumulation.

  Materials and Methods: In this clinical trial, we used 102 teeth covered with metal-ceramic and all-ceramic restorations. Before and after crowning, plaque index (PI) and gingival indexes (MGl) were measured. Data were analyzed using covariance (ANCOVA) test.

  Results: Measured PI and MGI (Mean±SD) in PFM Group prior to crowning were (1.96±0.38) and (1.45±0.48), respectively. In metal-ceramic restorations group, six months after crowning, measured PI and MGI (Mean±SD) were (1.22±0.49) and (1.82±0.61), respectively. Measured PI and MGI (Mean±SD) in All-Ceramic Group prior to crowning were (1.22±0.52) and (1.25±0.29), respectively. In All-Ceramic, six months after crowning, measured PI and MGI (Mean±SD) were (0.88±0.51) and (1.43±0.50), respectively. ANOVA test showed statistical significance difference between metal-ceramic and All-Ceramic Groups in Indexes (P<0.001).

  Conclusion: Metal-ceramic and All-Ceramic crowns were associated with inflammatory changes in gingival. Metal-ceramic restorations were associated with higher inflammatory indexes compared with All-Ceramic crowns.